California Geology

*Earth’s crust is divided into several tectonic plates that have moved over time across the surface of the earth.

Tectonic Plates are made of layer called lithosphere (crust and upper mantle) *These plates "float" on a thin underlying layer of magma in the upper mantle (asthenosphere).

California Mountain Formations Coastal Mountain Range Sierra Nevada Mtn. Range Subduction causes deep ocean trenches – off the coast of California. Heating caused by one plate diving beneath another forms volcanoes and may result in a curved chain (arc) of volcanoes Mountains are formed on the land

California has Earthquakes! Located where three tectonic plates come together. – Pacific Plate (moving towards the northwest 5.5 cm/year) – North American Plate, (moving more slowly towards the west) – Juan de Fuca Plate (small plate subducting under northwestern US)

San Andreas Fault Runs from the Salton Sea area to San Francisco area Transform Fault (plates slide past each other) “Big Bend” in the San Andreas Fault, north of Los Angeles. – Makes it difficult for the plates to slide past each other easily. – Stress builds up, then a big earthquake occurs

California has Volcanoes! Cascade Range – Lassen Peak and Mt. Shasta. Lassen Peak last erupted between 1914 and Shasta has erupted at least three times in the last 750 years, maybe as recently as 1786 – Past eruptions have sent flows of hot volcanic gases, ashes, cinders, and other debris down the slopes.

California has Volcanoes! Long Valley, in the Mammoth area of the Eastern Sierra – Located where magma from the mantle wells up into the crust.

California Grasslands Grassland (rangeland) resources Covers 25% of the state 90% of Calif. endangered species live in grassland Forage (feed) for livestock Lost when grassland is converted to cropland or cities (urbanization)

California has Wildfires Fire is a natural part of the grassland ecosystem Lightening and human activities can cause fires Wildfires occur because people have prevented fire for so long that there is a lot of dead plant material

California has Floods! Sacramento River used to flood Water flowed all the way through the San Joaquin Valley Dikes and levees built to hold water back so farms could be made Sacramento Bee January 14, 2011 “California has more risk of catastrophic storms than any other region in the country – even the Southern hurricane states, according to a new study released Thursday”

What is a dike or levee? Historically a dike is used prevent or control flood water from tidal bodies of water – system of dikes which protect the Netherlands. A levee diverts or restrains flood waters from rivers or streams – system of levees which protect cities along the Mississippi River.

Dikes and Levees Dikes and levees are built along water ways to protect the buildings from flooding Sometimes levees fail